"The Supreme Court cannot disqualify the prime minister like this," he said.
In the world of Pakistani politics, the court order against Gilani could become an advantage to his and Zardari's party in elections that have to be called before early next year. It will likely portray the case against Gilani as the latest in a long line of unjust decisions by the courts and the army and use it to fire up the party's base ahead of elections. Party founder Zulfikar Ali Bhutto was hanged by the court in 1979.
Rasul Bakhsh Rais, a professor at Lahore University of Management Science, said Zardari's government was unlikely to accept the court's decision.
"The political situation is not likely to be decided very peacefully I am afraid. It will be decided by demonstrations," he said.
If Gilani does not step down, the Supreme Court could call on the president or the military to enforce the decision, Rais said. "Pakistan is in a real mess."
Associated Press Writers Rebecca Santana and Munir Ahmed contributed to this report from Islamabad.